In conventional textile printing, a very large amount of water is consumed in the process. Water is involved during the fixation process of the printed dyes, and a massive amount of water is consumed to wash the fabrics of the excess dyes and auxiliary chemicals that remain in the textile after the fixation process. Until now, direct printing processes have been far from reaching 100% fixation yield for disperse dyes on polyester fabrics, which is one of the two most prominent chemistry-fabric combinations in the fashion industry.
Recent advances in digital textile printing have reduced the amount of water consumed. Digital printing requires less chemicals coming into contact with the surface of the textile during the printing process, and therefore requires less washing as a result. Nonetheless, the fixation yield is a problem that remains to be adequately addressed.
Furthermore, the low viscosity of inks used in digital textile printing requires specifically pre-treated fabrics. These pre-treated fabrics can require chemical auxiliaries be added to the fabric via a wet deposition method like foulard or spray coating processes with subsequent drying, each of which involves a significant amounts of water and energy. Ecological concerns exist regarding reduction of waste and waste water treatment, and thus a need exists to reduce the amount of water consumed in the digital printing of textiles.
Existing ink compositions cannot be efficiently used in direct inkjet printing processes without these pre-treatments, because the color fastness is not sufficient, and excessive rinsing is required to remove residual colorant. Examples of pre-treatment of textiles include pre-treatment with chemicals and surface modification, such as corona or plasma treatment. Examples of pre-treatment of textiles with chemicals for inkjet printing include those described in U.S. Pat. Nos. 8,236,385, 8,088,441, 6,962,735, 6,906,019, 6,698,874, 6,291,023, 6,001,137, 5,498,267, 4,725,849, 4,599,087, and U.S. Patent Application Pub. Nos. 2011/0169901 and 2006/0010619, each of which is incorporated herein in its entirety by reference.
A conventional direct textile printing on polyester fabric requires the following steps: 1) fabric pre-treatment to warrant sharp image quality and image vividness; 2) printing with a printing paste made of disperse water, dyestuff, dispersant, other textile printing auxiliaries and thickener to deliver the proper viscosity for printing; 3) fixation of the image by steaming, typically for 20 minutes in saturated vapor at 102° C.; 4) washing the textile to remove the unfixed dyes and chemicals from the surface of the fabric; 5) drying the textile.
Digital direct textile printing on polyester fabrics is similar to conventional direct textile printing and requires the following steps: 1) fabric pre-treatment to warrant sharp image quality and image vividness; 2) printing and image with a printing ink made of water, disperse dyestuff, dispersant, humectant, etc.; 3) fixation of the image by steaming, typically for 20 minutes in saturated vapor at 102° C.; 4) washing the textile to remove the unfixed dyes and chemicals from the surface of the fabric; 5) drying the textile.
A need exists for ink compositions suitable for use in a digital direct textile printing process for polyester fabrics, wherein the fabric need not be pre-treated, the image need not be treated with steam, the image fixation time is reduced, and the print quality is such that the textile passes the Oeko-Tex® Standard 100 without rinsing, thereby avoiding the washing and drying steps and the water and energy consumption associated therewith.
Many difficulties arise in preparing ink compositions for use in such a process. To avoid the pre-treatment of the polyester fabric, an ink composition must have physical and chemical properties such that it does not bleed when it contacts a polyester fabric which has not undergone pre-treatment. Furthermore, a pre-treatment process is typically required to incorporate the dye at a fixation yield approaching 100%, such as the pre-treatment currently used in printing for flags and banners, so the ink composition must have chemical properties such that, upon fixation, the dye preferentially diffused into the polyester fabric, and therefore leaves little to no dye in any residual ink composition carrier remaining after the fixation process. A need exists for ink compositions for use in direct inkjet printing which yield an image having a color fastness to water of at least 3 according to International Organization for Standardization test ISO 105-E01:2010 on a textile that has not been pre-treated.
Transfer printing does not have the same difficulties as direct printing, because the dye sublimes and leaves behind the entirety of its carrier on a transfer paper, thus the carrier does not impact the color fastness to water of the textile.